You have a problem with indexing. Every time you say V=Vnew, your V is simply replaced with a new overwritten value. You have an iteration ticker you call N, use it!
Now, your Decel phase has no time factor associated with it, so you'll need to look at that. Right now your test subject accelerates to a full stop in one iteration. Imagine the forces involved :D
clear; close all; clc
t(1) = 0.001; % time incriment in seconds
C = 0.008; % Drag constant
A = 30; % Accelleration part 1
Ad = -2; % Decelleration part 2
V = 0; % Velocity
N = 1; % iteration ticker
while true % Accel phase
Vnew=(V(N)+t*(A-C*V(N)^2));
if Vnew > 60
break
end
N = N+1;
V(N) = Vnew;
end
while true % Decel phase
Vnew=(Ad-C*V(N)^2); %get your timing into this term
if Vnew < 0
break
end
N = N+1;
V(N) = Vnew;
end
plot(V);
